BOSTON (AP) — Lawyers for reputed gangster James “Whitey” Bulger asked a judge Monday to delay opening statements in his racketeering trial so they can investigate a claim that law enforcement protected a hit man who is expected to be a star prosecution witness.

In a written motion, the defense said John Martorano, who admitted killing 20 people, has committed crimes since his 2007 release from federal prison and has been shielded from investigation.

Prosecutors opposed the delay, saying in a written response that the allegation was “thoroughly debunked” after an investigation. They said the complaint was made by a disgruntled state trooper who falsely accused another trooper of ignoring allegations against Martorano.

Judge Denise Casper did not immediately rule on the motion. The judge had said she hoped to have opening statements Wednesday.

The motion was filed as Casper began questioning potential jurors individually. Several people were excused after they said they had read books or media accounts about Bulger’s alleged crimes and had already formed an opinion that he is likely guilty. Several others were excused after they said it would be a financial hardship for them to serve on the trial, which is expected to last three to four months. Still others were excused after they told the judge they had booked a summer vacation.

Bulger, 83, the former leader of the Winter Hill Gang, is accused of a long list of crimes, including participating in 19 killings. He fled Boston in 1994 and was one of the FBI’s most wanted fugitives until he was captured in Santa Monica, Calif., in 2011.

Authorities say he was a longtime FBI informant who provided information on the New England Mafia, his gang’s main rivals. Bulger has pleaded innocent and denies being an informant.